With the development of new energy power batteries, the country encourages the development of high-density, high-power, and fast charging and discharging new energy vehicles. The original use of air-cooled cooling in new energy vehicles can no longer solve the problem of battery heat dissipation. The advantages of liquid cooling systems are fast cooling rate, good temperature uniformity, and simple fluid (temperature and flow) control. Liquid cooled cooling systems have become an inevitable trend for new energy vehicles. The thermal management system of the entire vehicle needs to be redesigned.
At present, the operating data of the liquid cooling system for battery packs (PACK) is blank, and new energy vehicle manufacturers are unable to design the liquid cooling system for the entire vehicle. Vehicle manufacturers need to understand the following data: 1) The reasonable temperature of the battery pack should be between 10-30 ℃. In low temperature weather, the liquid cooling system may reach -30 ℃. The battery pack itself has a heating block that preheats before starting to provide thermal protection. When the battery temperature exceeds 30 ℃ after driving, it needs to be cooled by the -30 ℃ liquid cooling system. How much liquid flow rate is required at this time? To ensure that the battery temperature is controlled within the range of 10-30 ℃ and that the pipe diameter of the automotive liquid cooling system is fixed, it is necessary to adjust the pressure to control the flow rate. Similarly, as the temperature of the car coolant changes, the flow rate and pressure of the coolant also need to change to ensure the battery temperature. 2） When it is hot weather, the temperature of the car coolant and battery pack may reach above 50 ℃. What are the charging and discharging conditions of the battery pack? How to match the cooling capacity of the entire vehicle refrigeration system (air conditioning space cooling, battery pack, electric drive, engine liquid cooling system) in order to achieve rapid balance in vehicle thermal management. Ensure that the overall performance and safety of the vehicle are within a reasonable range. The above data needs to be provided by our liquid cooling thermal testing platform.
Note: During the entire thermal testing process of the battery pack (PACK), the following equipment needs to work synchronously: charging and discharging equipment (BMS thermal management system), walk-in environmental box, thermal imager, etc.
The heat dissipation system in the new energy power battery pack can serve the purpose of cooling the new energy power battery pack. There are three cooling methods for new energy power batteries: air cooling, water cooling, and direct cooling. In the air-cooled mode, the cooling system utilizes natural air or fans, combined with the car's built-in evaporator, to cool the battery; In water cooling mode, the radiator is usually coupled with the refrigeration cycle system, and the heat of the battery is carried away by the refrigerant; In direct cooling mode, the heat dissipation system utilizes the principle of refrigerant evaporation latent heat to establish an air conditioning system in the entire vehicle or battery system. The evaporator of the air conditioning system is installed in the battery system, and the refrigerant evaporates in the evaporator and quickly takes away the heat of the battery system, thus completing the cooling operation of the battery system.
Air cooling technology
Air cooling technology is currently a widely used heat dissipation technology in new energy power batteries. Forced airflow can be generated through fans, as well as by utilizing headwinds or compressed air during the movement of a car. Compared with other technologies, air-cooled technology is relatively simple, safe, and easy to maintain. Toyota's hybrid electric vehicle Prius and Honda's Insight in Japan both use air cooling, while thermal management systems developed by car companies such as Nissan and General Motors mainly use forced air cooling.
Various types of new energy power batteries in China are basically equipped with air-cooled technology, which is basically equivalent to the level of foreign countries and can achieve good heat dissipation performance at low cost.
Compared with liquid cooling technology, air cooling technology has a lower heat exchange coefficient between the battery surface, slow cooling and heating speed, difficult control of temperature uniformity inside the battery box, difficult sealing design of the battery box, and poor dust-proof and waterproof effects.
Water cooling technology
The water-cooled cooling system mainly includes: electronic water pump, heat exchanger, battery heat sink, PTC heater, and expansion water tank.
Water cooling technology is a cooling technology based on liquid heat exchange, which is more efficient than air cooling technology. The internal temperature of the electric vehicle battery pack is more uniform, and it can be integrated with the vehicle's cooling system. The heat exchange coefficient between the battery wall is high, and the cooling and heating speed is fast. However, systems using water-cooling technology are more complex, heavy, difficult to repair and maintain, and there is a possibility of liquid leakage.
Water cooling technology has been studied early and applied for a long time abroad. With continuous exploration, practice, and improvement, the heat exchange coefficient and cooling and heating speed of the system have reached a good level. Moreover, through the application of new materials, the weight of foreign water cooling systems has also been reduced.
At present, water cooling technology is mainly used in car brands such as Tesla, General Motors Volt, French Peugeot Citroen, and BMW i3 abroad. The Tesla Model S model uses water-cooling technology to cool the battery. Tesla has carried out very in-depth design in its battery layout, thermal management system, and battery management system to ensure that each battery unit is under supervision, and its status data can be feedback and processed at any time. For individual small battery cells, Tesla independently seals them in steel compartments, and the liquid cooling system can specifically cool each cell, reducing the temperature difference between them and relatively reducing the risk of battery self ignition.
In recent years, with the continuous progress of new energy power battery cooling system technology in China, water-cooled products have gradually replaced air-cooled products.
According to the "Research Report on the Market Status and Investment Strategy of New Energy Power Battery Cooling Systems from 2017 to 2021" released by the Xinsijie Industry Research Center, relevant automobile manufacturers such as BYD and Geely have applied water-cooled products to their new energy vehicles. In the future, with the continuous advancement of industry technology, the combination of direct cooling and water cooling will become the main direction of market research and development.
A small number of new energy vehicles in China, such as the Jianghuai iEV7S, have adopted water-cooling technology. The iEV7S, a pure electric SUV powered by Jianghuai New Energy, utilizes water-cooling technology to control the temperature of the battery pack between 10-35 degrees Celsius. Even in ultra-low temperature environments of minus 30 degrees Celsius, it can charge normally without affecting its range. The new generation of battery pack water-cooling technology has achieved rapid low-temperature heating of the battery. Under environmental conditions of -30 ℃ and cell temperature of -15 ℃, the battery can be heated to above 10 ℃ in 40 minutes. At the same time, its excellent battery cooling performance meets the requirements of high-speed and fast charging continuous driving, and the high temperature of the battery is controlled below 35 ℃.
Researchers from Xinsijie Industry believe that in terms of air-cooled technology, China's technological level has reached the international level, and air-cooled heat dissipation systems have also been widely used in domestic new energy power battery heat dissipation systems. In terms of water cooling technology, due to technological limitations, China has only gradually had enterprises conduct research and production in recent years. Although technological progress is rapid, there is still a gap compared to foreign countries, and there is still significant room for improvement in the future.
In addition, the use of water-cooling technology can effectively solve the common problems faced by new energy vehicles, such as reduced low-temperature range and inability to charge at low temperatures, improve the user's driving experience, and promote the popularization of new energy vehicles. Based on this, water cooling technology will gradually replace air cooling technology in the future.